Continuous furnace for heating slabs or the like



Feb. 5, 1957 F. B. COFFMAN ETAL 2,780453 CONTINUOUS FURNACE FOR HEATINGSLABS OR THE LIKE Filed March 5, 1954 4 She'ets-Sheet few 6. COffMfl/Vand' fzam &Day/5 Nm NM N mm sm w m\ & V mm Feb. 5, 1957 F. B. COFFMANETAL & 2

CONTINUOUS FURNACE FOR HEATING SLAB S OR THE LIKE Filed March 5, 1954 4Sheets-Sheet 2 ?5 Inventari' FG'ED 5. (OFF/mm m/ flam 5 DHV/,

Feb. 5, 1957 F. B. COFFMAN ET AL CONTINUOUS FURNACE FOR HEATING SLABS ORTHE LIKE 4 Shets-Sheet 3 Filed March 5, 1954 %aki/fam@ Feb. 5, 1957 F.B. COFFMAN ETAL 2,780453 CONTINUOUS -FURNACE FOR HEATING SLABS OR THELIKE Filed March 5, 1954 4 Sheets-Sheet 4 F'IE- 7.

Ewan/tara: fim) B. .OFFMAW and Horo E. V/5,

%www/17 4 h be/r /%mey United States Patent O CONTINUOUS FURNACE FORHEATING SLABS OR THE LIKE Fred B. Coifman, Crown Point, and Floyd E.Davis, Gary, Ind.

Application March 5, 1954, Serial No. 414,:&80

6 Claims. (Cl. 263-6) This application is a continuation-in-part of ourcopending application, Serial No. 248,422, filed September 26, 1951.

This invention relates to a continuous furnace for heating metal slabsor the like to rolling or forging temperature, usually designated areheating furnace.

Reheating furnaces as usually constructed heretofore have had a solidhearth and have usually been fired from the discharge end, combustonoccurring solely in the space above the metal to be heated, and havebeen provided with a down-take flue at the charging end for the escapeof combustion gases. Thus the heat available at any point in the furnaceadjacent the charging end is dependent on the amount produced at a pointdistant therefrom. p

While numerous attempts have been made to improve the construction andoperating characteristics of such furnaces, they remain neverthelesssubject to several serious objections. In thevfirst place, the input ofheat to 'the charge is slow since the combustion gases which come incontact with the cold, freshly charged metal have already given up mostof their heat. By the time the metal reaches the region of maximumtemperature, therefore, it is heavily scaled and this retards furtherabsorption of heat. A considerable soakng period is thus necessary.

A further objection to known reheating furnaces is the difliculty ofadjusting them to take care of delays at the rolling mill. In case ofsuch a delay, there is danger of overheating the metal already charged,requiring discontinuance of firing, and a likelihood that metal chargedwhen operation is resumed will not be sufiiciently heated because thenormal firing rate may not be restored until the metal previously heatedis out of the furnace. In addition, the metal charged at the entranceend obstructs the down-take flue to some extent and the larger the slabsthe greater the obstruction, thus reducing the heat which it is possibleto generate at the very time when it should be increased. Finally, knownreheating furnaces have arched roofs of varying height. This makes forcostly Construction and maintenance, besides overheating of the chargeat points of minimum roof height and also washing the surfaces of theslab which ca'uses the accumulation of cinder on the hearth.

We have invented a reheating furnace for metal slabs or the like whichovercomes the aforementioned objections or greatly minimizes them. In apreferred embodiment, we provide a furnace divided into a number ofzones with burners firing transversely so that the amount of heatavailable at practically any point may be controlled independently ofthe rest of the urnace. After traversing the width of the furnace, thecombustion gases escape through down-take flues spaced along the furnaceon the side opposite the burners. A bale or sill along the flue sidedefines a waste-gas Pocket from which the flues descend. The furnace hasno hearth as such but is provided with water-cooled skids extending thefull length thereof at a level above the bottom or 5 V Patented Feb. 5,1957 'ice floor, along which slabs may slide. The burners are disposedin vertically spaced banks so that combustion of fuel takes place belowthe slabs as well as above whereby the latter absorb heat rapidly. Theskids are carred on water-cooled beams extending through the furnacefrom one side to the other. The beams rest on water-cooled columns orposts extending upwardly from water boxes spaced along the furnace anddisposed transversely thereof and below the bottom or floor. The furnaceroof may be flat and level throughout or arched from the front side(burner side) to the back side (flue side) or fiat and sloped or archedand sloped transversely of the furnace.

A complete Understanding of the invention may be obtained from thefollowing detailed description and explanation which refer to theaccompanying drawings illustrating the present preferred embodirnent. Inthe drawings,

Figure l is a partial longitudinal vertical section through our improvedfurnace showing parts in elevation;

Figure 2 is a cross-section taken on the plane of line II--II of Figure1; line I-I of Figure 2 indicates the plane on which the section ofFigure 1 is taken;

Figure 3 is a partial horizontal section taken on the plane of lineIII--III of Figure 2;

Figure 4 is a partial plan view of the skids on which the slabs slide intravelling through the furnace;

Figure 5 is a partial elevation thereof showing one of the transversebeams in section;

Figure 6 is a partial section taken on the line Vl-VI of Figure 5',

Figure 7 is a View similar to Figure 4 showing a modification; and

Figure 8 is a partial section taken on line VIII-VHI of Figure 7.

Referrng in detail to the drawings and, for the present, particularly toFgures 1 through 3, the furnace of our invention co-mprises an elongatedrefractory-lined chamber 10 including a floor 11, sides 12 and 13, aroof 14 and ends 15 and 16 of suitable brick. The binding (structuralmembers and plates) enclosing and supporting the brick walls of thefurnace is omitted. A charging opening 17 in end 15 is defined by awater-cooled lintel 18 and is normally closed by a vertically movablewatercooled door 19. Slabs 20 or the like are charged into the opening17 in single thickness and sidewise, i. e., with their length extendingtransversely of the chanber, and slide longitudinally therethrough onspaced skids 21, being pushed step-by-step by known means. The skidsextend the full length of the furnace and are located at a level abouthalfway between the floor and roof. A discharge opening 22 in end 16 isdefined by a watercooled lintel 23 and is normally closed by awater-copied door 24. The slabs, after passing through the chamber,descend a slide 25 onto a roller conveyor 26, the door 24 being openedfor the exit of successive slabs.

Skids 21 are composed of pipe and are arranged in spaced pairs. Aconnection 27 extends from one end of each to a source of cooling water.The skids rest on beams 28 also of pipe, extending transversely of thefurnace chambter and outwardly through the sides 12 and 13. The skidsare not secured to the beams but are free to slide thereon asnecessitated by expansion and contract ion, being confined laterally insaddles formed by short lengths of curved bar 29 welded to the beams ontheir upper side in spaced pairs, as clearly shown in Figures 5 and 6.Each beam is carried by tubular posts 30 extending upwardly through thefloor from a water box 31 disposed therebelow and provided with aconnection 32 to a source of cooling water. Posts 30 communicate withthe interior of the water boxes and the beams and consequently watersupplied to the boxes under pressure flows up through the posts, intothe beams and outof the ends of the latter. The` water boxes may alsoserve as beams on which the furnace chamber is carried, in addition tosupporting posts 30.

skids 21 have short lengths of round bar welded longitudinally to thetop thereof forming ribs 33, with which the slabs have contact insliding along the skids, the ribs on one skid of each pair beingstaggered relative to those on the other (see Figures 4 and 5). As aresult of this staggered relation, the same portion of a slab is notalways in contact with the supporting rib and all portions of the slabare exposed for heating during various portions of their travel throughthe chamber. The ends of the ribs nearer the entrance end 15 are beveledas at 34.

Transverse partitions 35 spaced along the length of chamber extend upfrom the floor thereof to about the level of skids 21, and divide thechamber into several zones, e. g., preheating, final heating, holding,soaking or temperature-controlling zones, and the amount of heatsupplied in each may be adjusted independently of all others. Theseveral zones are heated by flames fired t'ansversely of the chamber bymixer-type burners spaced along the length thereof and arranged invertically spaced banks, the upper burners being designated 36 and thelower 37. The former fire above the slabs on skids 21 and the lattcrbelow them. Pre-heated air is supplied to the burners from aconventional recuperator through headers 38 and 39 and individualconnections 40 each having a control valve 41 therein. Fuel is suppliedby valved connections 3811 by which the firing rate of each burner maybe adjusted to effect the independent control of the several zones asaforementionecl.

A longitudinal baflle wall 42 spaced inwardly of the side 13 of thechamber extends upwardly to about the same height as the partition wallsand forms pockets 43 for receiving waste combustion gases after theyhave traversed the width of chamber 10. The baflle wall also guides theproducts of combustion from the lower burners upwardly toward the slabson skids 21. Waste-gas down-take flues 44 spaced along the chamberextend downwardly from the pockets to a stack flue (not shown). Eachflue 44 preferably is provided with a damper 44a of known Constructionoperable independently to control the flow of combustion gasestherethrough.

The burners 36 and 37 in the several zones defined by partitions 35 andthe dampers in the waste-gas flues leading from each zone are adjustedto cause each slab to be subjected to a predetermined heating cycle asit advances through the chamber. The burners and dampers of thepre-heating and final heating zones are preferably adjusted for a higherfirng rate than those of subseqent zones in order to cause the slabs toabsorb the maximum amount of heat possible in the early stages of theheating cycle, i. e., before the formation of a scale layer ofsubstantial thickness, since the latter acts as an insulator and retardsfurther heat absorption. The exterior of the slab should be at rollingtemperature (about 2100 F.) by the time it has passed through the firsttwo zones. The remaining zones are fired at a lower rate in order topermit the soaking necessary to cause the heat to penetrate the interiorof the slab and become equalized throughout all portions thereof.

Figures 7 and 8 show a modified arrangement of ribs 33n on skids 21. Asshown, each skid has its ribs 33a alned in a plurality of rows, the ribsof adjacent rows being staggered relative to each other. This permitsthe number of skids to be reduced by one-half compared to thearrangement shown in Figures 2-6, yet preserves the advantage of freedomfrom cool spots or skid marks on the slabs which results fromalternating the lines of contact with supports, between differentportions of the slabs. The reduction in the number of skids means lessloss of heat from the furnace and lower initial cost as well. Thecorresponding ribs 33a of adjacent skids may be alined transversely ofthe furnace or staggered, so long as the ribs in adjacent rows on eachskid are staggered.

It Will be apparent from the foregoing that the furnace of our inventionis characterized by numerous advantages. In the first place, thetransversely firing burners above and below the path of the slabs, andthe separate, independently controllable heating zones make possible theheating of the steel at a higher rate in the early stages than possiblewith known reheating furnaces, thus shortening the overall heating timeand reducing the opportunity for free scaling to occur. The greaterflexibility in the temperature control provided by this method of zonefiring eliminates the solid hearth soaking zone and soaking period. Thequality of the heating is also improved, i. e., uniformity oftemperature throughout the slab, avoidance of washing, and theprevention of overheating during mill delays as wel] as the occurrenceof insufliciently heated slabs on resumption of operation after a delay.In other words, early and higher preheat assures faster heating and heatpenetration. This in turn elminates the required soaking period at thedelivery end of the furnace. The flexibility of control makes itpossible to hold all steel throughout the furnace indefinitely and thento immediately deliver steel at the proper rolling temperature after thedelay. The flexibility of control also makes it possible to heat withoutinterruption steels of varying composition which require differentheating cycles. The root of uniform contour (flat or arched) and height(whether sloped or level) eliminates hot spots and washing. The greateruniformity of temperature achieved, moreover, permits shortening orelimination of the soaking period. Greater efliciency of heating andlower cost thereof result directly from these advantages, and from thecheaper constructon and lower maintenance characteristic of our furnace.

Although we have disclosed herein the preferred embodiment of ourinvention, we intend to cover as well any change or modification thereinwhich may be made without departing from the spirit and scope of theinvention.

We claim:

1. A continuous furnace for heating slabs or the like comprising anelongated chamber, spaced parallel skids disposed therein at a levelabove the chamber floor and extending longitudinally thereof in asubstantially horizontal plane constituting a grid adapted to supportslabs during progressive movement through the furnace, a plurality ofspaced partition walls extending transversely of the chamber andupwardly substantially to the level of the skids, said partiton wallsdividing the chamber into a plurality of zones, a longitudinal verticalbaffle wall adjacent but spaced from one side wall of the chamber, saidbaflle wall extending upward only to about the level of said skids, saidpartition walls and said baflle wall forming pockets adjacent said oneside wall open at the top, one for each zone, a plurality of burnersspaced along said other side wall of the chamber above and below saidgrid, ring transversely thereof, there being at least one burner toreach Zone, a waste-gas flue extending from each pocket and a damper ineach flue whereby the flow of gases through said zones may beindependently controlled.

2. A continuous furnace as defined in claim 1, characterized by tubulartransverse beams spaced along said chamber and extending through theside walls thereof, supporting said skids, transverse water boxes spacedalong the chamber beneath the floor thereof, one for each beam, andtubular posts extending upwardly from said boxes supporting said beams,said posts communicating with the interior of both the boxes and beamspermitting the flow of cooling water from the former to the latter.

3. A continuous iurnace as defined in claim 1,' characterized by tubulartransverse beams spaced along said chamber and extending through theside walls thereof, supporting said skids, saddles at the points wherethe skids bear on the beams, each saddle comprising a pair of shortIengths of bar welded to the beams in spaced relation so that the skidsfit snugly but slidably therebetween.

4. A continuous furnace as defined in claim 3, charaeterized by saidbeans being cylindrical and said lengths of bar being bent to conform tothe transverse contour of the beams.

S. A continuous furnace as defined in claim 1, characterized by a row oflongitudinally spaced, alined, solid contact ribs welded on top of eachskid, the rbs in adjacent rows being staggered thereby exposing allportions of the bottom of each slab to combustion gases at least atintervals.

6. A continuous furnace as defined in claim 5, characterized by twoparallel rows of ribs on each skid.

References cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Trinks Industrial Furnaces, Volume 1, third edition,published by John Wiley and Sons, Incorporated, New York, New York,1934, pages 289 and 290.

